The method of the invention has been devised to be particularly useful in the manufacture of a particular form of printing plate. The invention is not, however, limited to such a use. At one stage during the production of the plate, sheet steel blanks of approximately 1m .times. 1/2m have to be passed through an oven to cure the tacky photopolymerisable material on the upper surface of the blank. This tacky material has been applied so as to have an extremely uniform thickness, typically 0.030 inch .+-.0.0015 inch. If the sheet is not maintained flat, the tacky material will flow from the high points of the sheet during drying and curing to reduce the uniform layer of tacky material to a useless non-uniform layer. It is thus a requirement of the manufacturing process that the sheet steel be maintained flat during the drying operation and in particular when the sheet is in an oven. One possible method of supporting the blank is to place it on a steel slab before it is passed into the oven. Unfortunately, the sheet tends to curl and has to be held down by adhesive tape. It has also been found that the slabs tend to distort and to become uneven during heating to temperatures as small as 100.degree. C. It is believed that the machining of the slab imparts heavy surface stresses into the material and as these are annealed out, the material distorts.
It is required, therefore, for the purposes of the invention to provide a support which does not distort on heating to temperatures of the order of 100.degree. C. and which is flat and planar over large areas.
The magnetic material may be a layer of elastomeric magnetic material. The elastomeric magnetic material may be adhesively bonded to the glass. The bond may be by means of double-sided adhesive tape.
The elastomeric material may be a sheet of rubber containing permanently magnetic particles.
The glass may be plate glass or float glass.
The present invention provides a method of supporting a sheet of magnetic material having a mobile tacky layer thereon which comprises the steps of:
1. locating the sheet of magnetic material on a support, the support comprising a sheet of glass having a flat planar surface with a uniform thickness layer of magnetic material thereon PA1 2. maintaining the glass horizontal and level.
The layer of glass and sheet material may be passed through a drying oven at a temperature below the Curie point for the magnetic material to cure or dry the magnetic material. The oven may be maintained at a temperature in the range 75.degree. C. to 175.degree. C.
The tacky material may be a photopolymerisable material, and the sheet material may be sheet steel. The tacky material may be sheet steel. The tacky material may have a viscosity in the range 1 to 1 .times. 10.sup.4 poises.
Further, according to the invention, in a method of drying and/or curing a layer of mobile tacky material on a magnetic sheet, there is provided the method of supporting the magnetic sheet upon a sheet of glass having a flat, planar surface and a uniform thickness layer of magnetic material on the flat planar surface. The magnetic material may be a layer of elastomeric magnetic material, such as a sheet of rubber containing permanently magnetic particles. The glass may be plate glass or float glass.